1. Field of the Invention
The present invention relates to an apparatus and method for dispensing detergent in a warewash machine, and more particularly to a probeless apparatus and method for dispensing detergent in a warewash machine.
2. Description of the Related Art
The present invention relates to an apparatus and method for supplying detergent into a commercial warewash machine. Such commercial warewash machines typically include a washtank for holding a supply of wash water, a wash water spray head for supplying the wash water to a rack of wares to be cleaned, and a rinse water spray head for rinsing the cleaned rack of wares. The wash water in the washtank should maintain a predetermined concentration of detergent to ensure that the dishes are properly cleaned.
During the wash cycle, a wash pump draws water that contains detergent from the washtank and by means of the wash water spray head supplies the wash water over the wares. Subsequent to the wash cycle which typically takes 45 seconds, a dwell period is provided between the wash cycle and an ensuing rinse cycle to permit the wash water solution to drain off the wares. Next, a rinse cycle that typically takes 12-15 seconds occurs. The fresh water rinse is supplied through the rinse water spray head. Typically, 1.25-2.5 gallons of fresh water are introduced during the rinse cycle. Food soils are carried down an overflow drain in the washtank by water that is displaced by the additional fresh water added during the rinse cycle. Thus, each time the rinse cycle occurs a certain amount of detergent is lost down the overflow drain.
Consequently, it is necessary to replenish the detergent each time the rinse cycle occurs to ensure that the desired concentration of detergent in the washtank is maintained. Also, in commercial operations it is common to completely drain the washtank two or three times in a 24 hour period. Each time the washtank is drained, it is necessary to charge the fresh water introduced into the washtank with detergent to achieve the desired concentration of detergent in the wash water. The fresh water introduced to fill the washtank after a draining operation can be supplied through the rinse water spray head or through a separate water source.
Two types of systems exist for introducing detergent into the washtank of a warewash machine. The first type is a probe system which operates by means of a conductivity sensing probe mounted in the washtank. This probe, when connected to a conductivity controller, senses the conductivity of the wash water in the washtank. When the conductivity drops below an adjustable, preset level, the conductivity controller activates a chemical feed pump to introduce additional detergent into the washtank. This type of system continues to add detergent until the conductivity of the wash water in the washtank is at or above a preset level. Once the conductivity gain drops below this preset level, the cycle repeats itself.
Although the probe systems are in common use in the industry, there are many drawbacks associated with such systems. For instance, factors other than the detergent concentration can affect the conductivity of the wash water in the washtank, thereby causing erroneous readings of the detergent concentration. Such factors include water hardness, water solids concentration, soil load and temperature. Also, mineral deposits such as limescale on the sensing probe can substantially reduce the accuracy of the system. Moreover, over extended periods of time, the set point of the sensing probe tends to vary. Finally, due to the number of factors that can affect the reading of the probe, the dispensing system cannot be calibrated prior to installation on a specific warewash machine. The inability to precalibrate the instrument complicates the installation process of the dispensing system.
A second known type of detergent dispensing system is referred to as a probeless system. Such systems are generally electro-mechanical in nature and typically include a variable speed peristaltic pump that is actuated by the rinse system of the warewash machine. This type of system adds detergent to the washtank of the warewash machine continuously during the entire rinse cycle.
Many problems exist with known probeless detergent dispensing systems. For example, such systems compensate only for the detergent lost during the rinse cycle. These systems do not compensate for the draining and refilling of the washtank and are not capable of pre-charging a newly filled washtank with the desired concentration of detergent prior to washing the first rack of wares. To compensate for the inability to precharge the washtank, the amount of detergent added during each rinse cycle is increased. This allows the system to compensate for its lack of pre-charge capability. However, the result is that the system provides an inadequate concentration of detergent for the first several wash cycles and an over-concentration of detergent for the remainder of ithe wash cycles. Also, because the detergent is introduced during the rinse cycle when fresh water is being added to the washtank, a portion of the newly introduced detergent is immediately carried by the rinse water down the overflow drain before it has an opportunity to disperse into the wash water. Thus, a certain amount of detergent is lost before it can be utilized.
Accordingly, it is an object of the present invention to provide an apparatus for dispensing a make-up amount of detergent after the rinse cycle has been completed.
It is another object of the present invention to provide a detergent dispensing system that can pre-charge a washtank with a desired concentration of detergent.
It is yet another object of the present invention to provide an apparatus that can distinguish between a rinse cycle and a fill cycle and add the correct amount of detergent based upon such a determination.
Still another object is to provide an apparatus and a method for dispensing detergent into a warewash machine that are economical and efficient, both in the cost of the apparatus and in the use of detergent.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, of may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.